WO2017205171A1 - Procédé et système lidar à détection directe avec transmission à modulation d'enveloppe de salves d'impulsions à modulation de fréquences (fm) échelonnées et démodulation en quadrature - Google Patents

Procédé et système lidar à détection directe avec transmission à modulation d'enveloppe de salves d'impulsions à modulation de fréquences (fm) échelonnées et démodulation en quadrature Download PDF

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Publication number
WO2017205171A1
WO2017205171A1 PCT/US2017/033271 US2017033271W WO2017205171A1 WO 2017205171 A1 WO2017205171 A1 WO 2017205171A1 US 2017033271 W US2017033271 W US 2017033271W WO 2017205171 A1 WO2017205171 A1 WO 2017205171A1
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Prior art keywords
signal
pulse
envelope
modulation
lidar system
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PCT/US2017/033271
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English (en)
Inventor
Kenneth V. Puglia
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Autoliv Asp, Inc.
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Priority to EP17726446.2A priority Critical patent/EP3436846A1/fr
Publication of WO2017205171A1 publication Critical patent/WO2017205171A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/08—Systems determining position data of a target for measuring distance only
    • G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
    • G01S17/26—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves wherein the transmitted pulses use a frequency-modulated or phase-modulated carrier wave, e.g. for pulse compression of received signals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/08—Systems determining position data of a target for measuring distance only
    • G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/42—Simultaneous measurement of distance and other co-ordinates
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/50—Systems of measurement based on relative movement of target
    • G01S17/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/88—Lidar systems specially adapted for specific applications
    • G01S17/93—Lidar systems specially adapted for specific applications for anti-collision purposes
    • G01S17/931—Lidar systems specially adapted for specific applications for anti-collision purposes of land vehicles
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/481—Constructional features, e.g. arrangements of optical elements
    • G01S7/4817—Constructional features, e.g. arrangements of optical elements relating to scanning
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G01S7/484—Transmitters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G01S7/486—Receivers
    • G01S7/4865—Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G01S7/486—Receivers
    • G01S7/487—Extracting wanted echo signals, e.g. pulse detection

Definitions

  • the present disclosure is related to LiDAR systems and, in particular, to a direct detection LiDAR system and method with step-FM pulse-burst envelope modulation
  • LiDAR is commonly referred to as an acronym for light detection and ranging, in the sense that LiDAR is commonly considered an optical analog to radar.
  • incoherent LiDAR also commonly referred to as direct detection or direct energy detection LiDAR, primarily uses an amplitude measurement in light returns, while coherent LiDAR is better suited for phase- sensitive measurements or other more sophisticated transmitter waveform modulation techniques.
  • Coherent systems generally use optical heterodyne detection, which, being more sensitive than direct detection, allows them to operate at a much lower power and provide greater measurement accuracy and resolution, but at the expense of more complex transceiver requirements and cost.
  • a LiDAR system includes a signal generator for generating an output signal having a variable frequency.
  • a modulation circuit receives the output signal from the signal generator and modulates the output signal to generate a pulsed modulation envelope signal configured to comprise a plurality of pulses, two or more of the plurality of pulses having two or more respective different frequencies.
  • the modulation circuit applies the pulsed modulation envelope signal to an optical signal to generate a pulse-envelope-modulated optical signal comprising a plurality of pulses modulated by the pulsed modulation envelope signal.
  • Optical transmission elements transmit the pulse-envelope-modulated optical signal into a region.
  • Optical receiving elements receive reflected optical signals from the region.
  • Receive signal processing circuitry receives the reflected optical signals and uses quadrature detection to process the reflected optical signals.
  • the modulation circuit comprises a pulse modulator for modulating the output signal from the signal generator to generate the pulsed envelope modulation signal.
  • the modulation circuit can include a laser modulator for applying the pulsed modulation envelope signal to an optical signal to generate the pulse-envelope-modulated optical signal.
  • the modulation circuit comprises a laser modulator for applying the pulsed modulation envelope signal to an optical signal to generate the pulse- envelope-modulated optical signal.
  • the pulsed modulation envelope signal comprises two or more consecutive pulses at the same frequency.
  • the pulsed modulation envelope signal comprises one and only one pulse at each of a plurality of frequencies.
  • the optical receiving elements comprise a microelectromechanical systems (MEMS) scanning mirror for scanning the region to receive the reflected optical signals from the region.
  • MEMS microelectromechanical systems
  • the reflected optical signals from the region can be received through a series of scans of the MEMS scanning mirror.
  • Each of the series of scans can provide receiver coverage over a field of view of the LiDAR system, each scan receiving reflected signals of a single frequency of the pulsed modulation envelope signal.
  • the two or more different frequencies increase with time.
  • the two or more different frequencies decrease with time.
  • the LiDAR system is installed and operates in an automobile.
  • FIG. 1 includes three curves which illustrate transmitter envelope modulation techniques, using a substantially sinusoidal modulation envelope, as applied to direct detection LiDAR.
  • FIG. 2 includes three curves which illustrate transmitter envelope modulation techniques, using a pulse burst modulation envelope, as applied to direct detection LiDAR.
  • FIG. 3 includes three curves which illustrate transmitter envelope modulation techniques, using linear frequency envelope modulation, as applied to direct detection LiDAR.
  • FIG. 4 includes a schematic functional block diagram of a quadrature demodulation system and technique, according to some exemplary embodiments.
  • FIG. 5 includes a schematic functional block diagram of a conventional direct detection LiDAR system.
  • FIG. 6A includes a schematic functional block diagram which illustrates a LiDAR system using step-FM pulse-burst transmit envelope modulation and quadrature demodulation, according to some exemplary embodiments.
  • FIG. 6B is a schematic diagram illustrating detail of the step-FM pulse-burst modulation signal used in the system of FIG. 6A, according to some exemplary embodiments.
  • FIGs. 7 A and 7B include schematic diagrams of step-FM pulse-burst envelope modulation waveforms, according to some exemplary embodiments.
  • FIGs. 8A and 8B include schematic diagrams of step-FM pulse-burst envelope modulation waveforms, including single-frequency and two-frequency envelope modulation waveforms, respectively, according to some exemplary embodiments.
  • FIG. 9 includes a schematic diagram illustrating the data acquisition process as related to the step-FM pulse-burst envelope modulation waveform, according to some exemplary embodiments.
  • FIG. 10 includes a schematic diagram of a step-FM pulse-burst waveform data matrix, according to some exemplary embodiments.
  • FIG. 11 includes a schematic diagram illustrating FFT implementation of a filter bank of N filters, according to some exemplary embodiments.
  • FIG. 12 includes a table of parametric data in a typical automotive operational scenario of a LiDAR system, according to some particular exemplary embodiments.
  • FIG. 13 includes a schematic diagram graphically illustrating results of a processing gain simulation using a 256-point FFT for purposes of the simulation, according to some exemplary embodiments.
  • FIG. 14 includes a schematic functional block diagram which illustrates a LiDAR system using step-frequency -modulation (FM) pulse-burst transmit envelope modulation and quadrature demodulation and a MEMS scanning mirror, according to some exemplary embodiments.
  • FM step-frequency -modulation
  • FIG. 15 includes a detailed schematic diagram illustrating MEMS scanning mirror transmit beam pattern as employed in the LiDAR system of FIG. 14, according to some exemplary embodiments.
  • FIG. 16 includes schematic time diagrams illustrating the data acquisition process of the LiDAR system of FIGs. 14 and 15, utilizing a MEMS scanning mirror, according to some exemplary embodiments.
  • FIG. 17 includes a schematic detailed functional block diagram of a MEMS mirror controller/driver illustrated in FIG. 14, according to some exemplary embodiments.
  • FIG. 18 includes a schematic time diagram illustrating synchronization of step-FM modulation pulses with scanning mirror position provided by MEMS the mirror controller/driver of FIGs. 14 and 17, according to some exemplary embodiments.
  • FIGs. 19A through 19D include a series of four illustrative data matrices for the scanning mirror data acquisition, according to some exemplary embodiments.
  • FIG. 20 includes a table of parametric data in a typical automotive operational scenario of a LiDAR system using a MEMS scanning mirror for data acquisition, according to some particular exemplary embodiments.
  • FIG. 21 includes a schematic perspective view of an automobile equipped with one or more LiDAR systems described herein in detail, according to some exemplary embodiments.
  • FIG. 22 includes a schematic top view of an automobile equipped with two LiDAR systems as described herein in detail, according to some exemplary embodiments.
  • Direct detection LiDAR systems are characterized by construction and functional simplicity and, unlike the more complex homodyne or heterodyne LiDAR systems, do not utilize frequency translation or down conversion stages, which facilitate signal detection and processing gain advantages.
  • the signal detection and processing gain advantages of homodyne/heterodyne LiDAR systems are enabled by advanced modulation and coding of the transmitted signal combined with sophisticated correlation processing techniques within the LiDAR receiver.
  • Transmit signal modulation and coding in conjunction with advanced correlation processing techniques, have been utilized within radar systems, from complex military object imaging systems to commercial automotive autonomous cruise control applications.
  • LiDAR systems with the exception of very advanced measurement requirements, e.g. NASA measurements of CO2 emissions, have not utilized these techniques.
  • development of laser transmit signal envelope modulation and quadrature demodulation of the recovered envelope modulation signal has exhibited similar advantages to those associated and achieved via the radar science.
  • Laser transmitter envelope modulation and quadrature demodulation represent a modest increase in complexity of direct detection LiDAR systems with significant benefits in measurement capability and lower operational power by enabling signal processing gain to direct detection LiDAR.
  • laser transmitter envelope modulation and receiver quadrature demodulation techniques are applied to direct detection LiDAR systems.
  • the laser transmitter envelope modulation is a step-FM pulse-burst laser transmitter envelope modulation.
  • Data acquisition techniques and processing gain associated with the step-FM pulse-burst laser transmitter envelope modulation are also described herein in detail.
  • FIG. 1 includes three curves which illustrate a general instance of transmitter envelope modulation techniques, using a substantially sinusoidal modulation envelope, as applied to direct detection LiDAR, according to exemplary embodiments.
  • a modulation envelope signal, a sinusoidal carrier signal and an envelope-modulated carrier waveform are illustrated.
  • the mathematical definitions associated with the envelope modulation waveform, carrier and transmit envelope modulated waveform are in accordance with the following equation (1):
  • Mod(t) sin(27if m t) ⁇ modulation waveform
  • Car(t) sin(2;z c t)— » carrier (1)
  • T x ⁇ t) Mod(t) ⁇ Car(t)— » envelop modulated carrier
  • envelope-modulated carrier implies multiplication of the modulation waveform and the carrier signal.
  • the direct detection LiDAR system performs the multiplication within the laser modulator element as described below in detail.
  • the envelope modulation technique results in transmission of both sidebands.
  • FIG. 2 includes three curves which illustrate transmitter envelope modulation techniques, using a pulse burst modulation envelope, as applied to direct detection LiDAR, according to other exemplary embodiments.
  • a modulation envelope signal, a sinusoidal carrier signal and an envelope-modulated carrier waveform are illustrated.
  • a repetitive pulse waveform modulates the carrier.
  • Laser modulators are capable of pulse modulation at very high repetition frequencies, e.g., several hundred megahertz, which facilitates coherent detection of the recovered modulation waveform with attendant signal processing benefits as will be described in detail herein.
  • the position in time of the modulating pulses may be a variable, which allows for pulse position modulation (PPM) coding.
  • PPM pulse position modulation
  • FIG. 3 includes three curves which illustrate transmitter envelope modulation techniques, using linear frequency envelope modulation, as applied to direct detection LiDAR, according to other exemplary embodiments.
  • a modulation envelope signal having a linear variation in frequency, a sinusoidal carrier signal and an envelope-modulated carrier waveform are illustrated.
  • FIG. 3 illustrates linear frequency envelope modulation, where, in this particular exemplary embodiment, the modulation waveform frequency is linearly changed from fi to (AF) over a specific time interval ( ⁇ ).
  • the linear frequency modulation envelope is advantageous for the implementation of FMCW LiDAR due to the ability to provide high-range resolution in accordance with the frequency deviation (AF), lower detection bandwidth and the unique spectral resolution properties of the Fast Fourier Transform (FFT) computation technique.
  • AF frequency deviation
  • FFT Fast Fourier Transform
  • One principle of transmitter envelope modulation is that upon transmission, the modulation envelope is subject to phase delay in accordance with the envelope frequency.
  • the total transmission phase shift in the two-way range from LiDAR system to object is described by the following e uation (2):
  • the amplitude and transmission phase of the modulation envelope are demodulated in the quadrature demodulator.
  • the step-FM pulse burst envelope modulation waveform LiDAR is described in detail below.
  • the step-FM pulse burst envelope modulation waveform as applied to direct detection LiDAR, in accordance with the present disclosure is particularly advantageous for high -range resolution applications where object detection parameters allow the employment of modest bandwidth data acquisition.
  • the step-FM pulse waveform receiver of the present disclosure requires a nominal narrow bandwidth receiver and modest sampling rate for the analog-to-digital conversion process.
  • FIG. 4 includes a schematic functional block diagram of a quadrature demodulation system and technique, according to some exemplary embodiments.
  • Quadrature demodulation is an efficient detection technique which utilizes the advantages of coherent signals to provide the orthogonal, or vector signal components of a modulated signal.
  • Quadrature demodulation is universal in the sense that it has the ability to recover amplitude modulation (AM), frequency modulation (FM) and phase modulation (PM) components of a modulated signal.
  • AM amplitude modulation
  • FM frequency modulation
  • PM phase modulation
  • a quadrature demodulator includes a coherent, continuous wave (CW) local oscillator (LO) signal at the modulated carrier input frequency fo, a 0°/90° power divider, the in-phase and quadrature-phase mixers, and low-pass filters to eliminate the LO signal and other spurious signals from the demodulated output, which is provided at an I-channel output and a Q-channel output as shown.
  • CW continuous wave
  • LO local oscillator
  • low-pass filters to eliminate the LO signal and other spurious signals from the demodulated output, which is provided at an I-channel output and a Q-channel output as shown.
  • a single-frequency source is utilized for both envelope modulation and quadrature demodulator LO.
  • FIG. 5 includes a schematic functional block diagram of a conventional direct detection LiDAR system 50.
  • a typical operational configuration involves the transmission of a high-power laser transmit pulse of short duration, typically 2.0 to 20 nanoseconds, at transmit optics 52, via light emitter 66, modulated under the control of a digital signal processor and control (DSPC) 68 by laser modulator 64.
  • DSPC digital signal processor and control
  • the received signal is then amplified by the transimpedance amplifier (TIA) 58 and filtered by a low-pass filter (LPF) 60.
  • the analog-to-digital converter (ADC) 62 samples range bins commensurate with the pulse width.
  • ADC analog-to-digital converter
  • DSPC 68 if a signal is determined to exceed a specific threshold level within a specific range bin, a target is declared.
  • Other processing strategies may be employed to improve the signal-to-noise ratio, e.g., range bin sampling following multiple transmitter pulses and integration of the received signal energy from each transmitted pulse, also known as non-coherent detection; however, the basic operation is limited to high-power pulse transmission and receive signal detection and amplification.
  • a time-of-flight (TOF) system transmits multiple pulses in the form of a square-wave and utilizes a phase detector on receive to measure the two-way time of flight.
  • the time-of-flight system must limit the square-wave modulation frequency in order to avoid phase ambiguity.
  • FIG. 6A includes a schematic functional block diagram which illustrates a LiDAR system 100 using step-frequency -modulation (FM) pulse-burst transmit envelope modulation and quadrature demodulation, according to some exemplary embodiments.
  • FM step-frequency -modulation
  • FIG. 6B is a schematic diagram illustrating detail of one pulse of the step-FM pulse-burst modulation signal 115 used in system 100 of FIG. 6 A, according to some exemplary
  • the burst frequency is a step-FM envelope sequence, characterized by incremental step change in frequency Af.
  • the frequency step sequence continues for n frequency steps, producing a total frequency deviation of n x Af.
  • the modulation frequency is coherent with the recovered envelope on receive, thereby providing an efficient means of modulated signal detection.
  • a band-pass filter centered at the arithmetic mean of the burst frequency attenuates the broadband noise of the TIA, and also the l/f noise associated with the photo- detector and TIA.
  • a quadrature demodulator is employed to recover pulse burst envelope and attendant two-way transmission phase shift of the modulation envelope.
  • LiDAR system 100 includes receive optics 154 at which optical energy, including optical returns from one or more target objects, are received.
  • the optical energy is received from receive optics 154 at a light detector 156, which converts the received optical energy to one or more electrical signals, such as, for example, the illustrated square wave signal.
  • the electrical signals are amplified by TIA 158 and filtered by BPF 160, having a center frequency at the burst modulation frequency fi to fcate.
  • the resulting amplified and filtered signal illustrated in FIG. 6A as a substantially sinusoidal signal, is applied at node 161 to first inputs of I/Q mixers 162, 164.
  • the modulating step-FM signal is generated by a step-FM source, which includes a voltage-controlled oscillator (VCO) 182 under the control of a control signal from phase-locked loop (PLL) control circuit 183, which is in turn controlled by DSPC 168 via a control signal on line 181.
  • VCO voltage-controlled oscillator
  • PLL phase-locked loop
  • the output signal of VCO 182 is applied to a power splitter 184, which splits the signal and provides the split signal at two outputs.
  • the first output 185 is routed to splitting and phase shifting circuitry or 90-degreee power splitter 186, which splits the signal, applies a phase shift to one of the resulting split signals, and generates a pair of output signals being offset in phase.
  • a 90-degree phase shift is applied to one of the signals, such that splitting and phase shifting circuitry or 90-degreee power splitter 186 generates a first "in-phase” local oscillator (LO) signal 189 and a second "quadrature-phase” or “quadrature” LO signal 191, which is shifted in phase by 90 degrees with respect to in-phase LO signal 189.
  • the in-phase and quadrature-phase LO signals 189, 191 are applied to second "L" inputs of I/Q mixers 162, 164, respectively.
  • I/Q mixers 162, 164 mix the amplified and filtered input signal at node 161 applied at first "R" inputs of I/Q mixers 162, 164 with the in-phase and quadrature-phase LO signals 189, 191, respectively, to generate output signals 193, 195, respectively, which are low- pass filtered by low-pass filter (LPF) 166 and LPF 168, respectively.
  • LPF low-pass filter
  • the resulting filtered analog signals are converted to digital signals by analog-to-digital converters (ADC) 170, 172, respectively, and sampled under the control of sample control signal 197, which is generated by DSPC 168.
  • ADC analog-to-digital converters
  • the resulting sampled digital I/Q (quadrature) signals i.e., I-channel and Q-channel signals, 105, 107 are processed by DSPC 168 to determine range and/or velocity of the one or more target objects.
  • Results of this detection processing performed by DSPC 168 can be forwarded as desired, such as, for example, to a user interface, via a system interface 109.
  • the second output 187 of power splitter 184 is routed to a pulse modulator 174, which converts the substantially sinusoidal signal 187 from power splitter 184 to a pulsed substantially sinusoidal signal 111.
  • the timing of pulses in the pulsed sinusoidal signal 111 is controlled by step-FM pulse-burst modulation signal 115 on output signal line 113 from DSPC 168. That is, step-FM pulse-burst modulation signal 115 is used by pulse modulator 174 to modulate substantially sinusoidal signal 187 to generate pulsed substantially sinusoidal signal 111.
  • the resulting pulsed modulated signal 111 from pulse modulator 174 is applied as a modulation signal to a laser modulator 176, which generates a control/modulation signal 117, which is applied to light emitter 178 to generate a step-FM pulse- burst modulated optical signal, which is transmitted to transmit optics 180, by which the step-FM pulse-burst modulated optical signal is transmitted to the one or more target objects.
  • the quadrature detection precedes analog-to- digital conversion.
  • the quadrature detector recovers the pulse modulation envelope associated with the low-frequency pulse modulation.
  • the data samples are subsequently processed via spectral resolution or other means of each range bin data set.
  • the spectral resolution approach used reduces the detection bandwidth and effectively integrates the energy of the range bin sample set.
  • FIGs. 7A and 7B include schematic time diagrams of step-FM pulse-burst envelope modulation waveforms, according to exemplary embodiments.
  • FIG. 7A illustrates the step-FM pulse-burst modulation waveform in the case of a single pulse burst dwell with consecutive frequency increments.
  • FIG. 7B illustrates the step-FM pulse-burst modulation waveform in the case of multiple bursts at each of a plurality of frequencies, i.e., the pulse bursts are grouped in a series of fixed-frequency clusters. That is, exemplary step-frequency pulse burst envelope modulation waveforms according to the present disclosure are graphically illustrated in FIGs.
  • FIG. 7A and 7B where consecutive steps are separated in frequency by Af in FIG. 7A, and a cluster of k, fixed-frequency pulse bursts are represented before advancing in frequency by Af to the next cluster in FIG. 7B.
  • the consecutive frequency increments of FIG. 7 A provide rapid detection of objects within the illumination volume of the transmit and receive optics, while the fixed-frequency cluster of FIG. 7B provides the capability of additional processing gain via additional received signal integration from each cluster.
  • the increased number of pulses increases cycle time.
  • S R signal-to- noise ratio
  • a combination of the approaches of FIGs. 7 A and 7B can be used, for example, using the relatively fast scan of FIG. 7A for close-range monitoring and the scan according to FIG. 7B for longer-range monitoring.
  • the number of frequency steps may include a single frequency or two- frequency frequency shift keying (FSK), and may be utilized separately or in conjunction with the consecutive or cluster sequences.
  • FIGs. 8A and 8B include schematic time diagrams of step- FM pulse-burst envelope modulation waveforms, including single-frequency and two-frequency envelope modulation waveforms, respectively, according to exemplary embodiments.
  • the single frequency of FIG. 8 A is applicable to the measurement of Doppler frequency, which enables relative velocity measurement between LiDAR system 100 and target objects.
  • the FSK or two- frequency sequence of FIG. 8B is also advantageous with respect to Doppler frequency measurement.
  • the reduced transmission bandwidth of single-frequency or two-frequency FSK although facilitating Doppler frequency measurement, limits high resolution range measurement, as disclosed by the range resolution Equation 3 :
  • a significant advantage of the step-FM pulse-burst envelope modulation waveform is the high range resolution capability provided by the transmission bandwidth, n-Af, and modest bandwidth data acquisition.
  • the ability to detect the change in two-way transmission phase of the step-frequency envelope modulation signal is the basis for high-range resolution
  • Detection of the step-frequency envelope phase shift is a consequence of the coherent detection process of the quadrature demodulator, according to exemplary embodiments.
  • pulse burst refers to the shape of the modulation envelope signal, that is, the signal that modulates the optical carrier, examples of which are illustrated in the time diagrams of FIGs. 7A and 7B.
  • the term “pulse” refers to the feature of the envelope signal that it is “active” for a certain period of time (x w ) and “inactive” in the time between pulses.
  • the thin, vertical rectangular hashed regions in FIGs. 7A and 7B are "pulses,” as described herein.
  • Fig. 6B illustrates the detail of one pulse of duration x w having a burst of frequency f n and, therefore, a period as illustrated of l/f n .
  • consecutive pulses include a "burst" at a frequency f that increases ("increments") by Af at each consecutive pulse, as illustrated in FIG. 7 A.
  • the pulses are part of a longer "dwell” or “fixed frequency cluster” in which multiple consecutive pulses have bursts at the same frequency f, as illustrated in FIG. 7B.
  • the frequency f of consecutive clusters of same-frequency bursts increases ("increments") by Af at each consecutive cluster of pulse bursts. That is, "burst” refers to the periodic signal at f within each "pulse.”
  • FIG. 9 includes a schematic diagram illustrating the data acquisition process as related to the step-FM pulse-burst envelope modulation waveform, according to exemplary embodiments.
  • FIG. 9 represents the filling of a data matrix (set) following successive transmission pulses.
  • the first stage in the step-FM pulse burst envelope modulation LiDAR system signal processing is acquisition of a data set which represents the signal level of each range bin at the output of each channel of the quadrature demodulator from successive transmission pulses.
  • a frame is defined as a single transmission pulse burst ( Tw), followed by a receive interval (7 ⁇ &) during which the ADC 170, 172 acquires a sample from each channel of the quadrature demodulator output at each range bin.
  • a range bin is defined in accordance with the pulse burst width (r w ), which sets the preprocessing range measurement resolution.
  • R is the range resolution (4)
  • T W is the pulse burst width
  • FIG. 9 which may represent an I-channel or Q-channel signal
  • the arrows designate sample points of the ADCs 170, 172.
  • a variable-amplitude return signal is noted in range bin 12.
  • the variable amplitude is a consequence of coherent detection of the change in phase due to the change in frequency of successive transmission pulse bursts.
  • a principle of transmitter envelope modulation is that upon transmission, the modulation envelope is subject to phase shift in accordance with the envelope modulation frequency.
  • the total envelope transmission phase associated with the two-way range to an object may be written at frequency, fo.
  • the reflected signal from an object at range R assuming that the transmitted signal is a co- sinusoidal with zero phase reference, may be written
  • the reflected signal is applied to the quadrature demodulator and converted to in-phase and quadrature-phase video signals as represented within the following Equation 10:
  • the coefficient, a is the loss associated with the two-way path loss, the transmission and receive optics, and object reflectivity.
  • step-FM waveform There are three constraints with respect to the step-FM waveform. These include the following.
  • the duration of the step frequency increment (At) must be equal to or greater than the two-way time-of-flight between the LiDAR system and object at the maximum range of operation. Stated mathematically:
  • the pulse burst repetition interval (3 ⁇ 4) must be greater than the two-way time-of-flight to the range at which the highest signal level is expected. Stated mathematically:
  • constraints 1 and 2 are related to the maximum operational range, Raise therefore, for a maximum operational range of 150 meters, for example, the maximum frequency step increment is 1.0 MHz, and the minimum step frequency dwell time is 1.0 ⁇ If the highest signal level from an object is expected at 300 meters, the pulse burst repetition interval must be greater than 2.0 ⁇
  • FIG. 9 represents range bin signal data at either of the quadrature demodulated outputs (I-channel or Q-channel) at a particular range bin. It is noted that a bipolar video signal appears in range bin 12, which indicates the presence of an obj ect; as contrasted with receiver noise only in other range bins.
  • ADCs 170, 172 digitize each of the I-channel and Q-channel sampled range bins and subsequently fill, or populate, the locations of a dimension (n x N) data matrix as illustrated in FIG. 10, which is a schematic diagram of a step-FM pulse-burst waveform data matrix, according to some embodiments.
  • enhancement of the detection process can be performed to provide accurate object range and velocity measurements.
  • detection enhancement is accomplished via exploitation of the data matrix using available signal processing techniques.
  • the columns of the n x N data matrix represent range bin signal level from multiple transmission pulses, which may be summed through the process of coherent integration.
  • Coherent integration adds the signal level from multiple pulses and effectively increases the signal-to-noise ratio. This is significant because LiDAR object measurement error variance is reduced in direct proportion to the signal-to-noise ratio.
  • spectral resolution may be performed to effect increase to the signal-to-noise ratio.
  • the sample data from objects is mathematically represented by sinusoidal signals as a result of the change in transmission phase of the modulation envelope.
  • Spectral resolution of the column data is executed in accordance with the Discrete Fourier Transform (DFT), as defined within the following Equation 15:
  • the Fast Fourier Transform is a computationally efficient process for the calculation of the DFT, which implements a set of n identical filters, or filter bank, distributed uniformly over the frequency domain at intervals of 1/nT, where Jis the time interval over which n samples of a waveform have been acquired.
  • the FFT is particularly well suited to spectral resolution in FM radar and LiDAR instrumentation because the data processing requires a filter bank which may be implemented numerically with a modest-capability digital signal processor (DSP), programmable logic device (PLD), or field-programmable gate array (FPGA).
  • DSP digital signal processor
  • PLD programmable logic device
  • FPGA field-programmable gate array
  • FIG. 11 includes a schematic diagram illustrating FFT implementation of a filter bank of N filters, according to some exemplary embodiments.
  • the graphic of FIG. 11 illustrates the filter bank attributes of the FFT.
  • the impact of the filter bank is significant because the signal energy from each detected object is concentrated within a single filter of the filter bank to the extent of the range resolution. Also of significance is the reduction in the noise detection bandwidth ifs/ri) which improves the signal-to-noise ratio.
  • the spectral resolution filter bank of FIG. 11 represents specific range bin signal level content.
  • the signal level of each range bin filter is examined to determine if the signal level exceeds a predetermined threshold level; whereupon, a binary object decision is executed with respect to "presence” or "absence.”
  • the range bin signal level is utilized as constituent elements of a point-cloud data set, for example, an object surface map or image.
  • enhancing processing gain such as by increasing signal- to-noise ratio within direct detection LiDAR systems offers significant benefits with respect to system operational parameters and, in particular, measurement accuracy and detection range.
  • Signal processing gain is a direct result of the combination of transmit envelope modulation and coherent, quadrature demodulation, according to the present disclosure. Specific attributes pertaining to step-FM pulse-burst transmit envelope modulation and quadrature demodulation are described herein in detail. The data acquisition process and spectral resolution signal processing of the exemplary embodiments are described herein in detail.
  • the columns of the data matrix of FIG. 10 contain numerical values which have been acquired following transmission of each step frequency pulse burst via sampling of the individual range bins.
  • the samples represent a sinusoidal signal at a frequency proportional to the step frequency, , and the range to the object, R.
  • the applicable Equations (8) and (9) are repeated and modified to reflect quadrature demodulation (down conversion) here for
  • the frequency variable has been indexed in accordance with the transmission frequency at the sample time of the ADCs 170, 172; and that the amplitude coefficients have been primed ) to indicate the receiver gain.
  • the transformation of range-to-frequency has been implemented.
  • Spectral resolution of the range bin samples, the data matrix columns, may be utilized to increase the signal energy via effective pulse integration and reduction of the noise detection bandwidth, thereby enabling processing gain.
  • FIG. 12 includes a table of parametric data in a typical automotive operational scenario of LiDAR system 100, according to some particular exemplary embodiments.
  • object dwell time is calculated for the pre-processing range resolution of 15 meters, as an illustrative example.
  • Data acquisition time 0.512 msec
  • FIG. 13 includes a schematic diagram graphically illustrating results of a processing gain simulation using a 256-point FFT for purposes of the simulation, according to exemplary embodiments.
  • simulation of the processing gain illustrates 25.1 dB of signal-to-noise ratio increase.
  • FIG. 13 also simulates the range measurement resolution for object separated in range by 2.0 meters, as an exemplary illustration, It is noted that two objects, separated by 2.0 meters, for example, are readily discerned, which validates the post-processing range resolution estimate.
  • each object was introduced at 0.0 dB signal-to-noise ratio. Zero-mean Gaussian noise was used for the noise component.
  • a fundamental feature of transmitter envelope modulation is that upon transmission, the modulation envelope is subject to phase delay in accordance with the envelope modulation frequency. Upon recovery of the modulation envelope in the photo detector diode, the amplitude and transmission phase of the modulation envelope are detected within the quadrature demodulator.
  • the LiDAR system can include a
  • MEMS scanning mirrors for enhancing processing of optical signals.
  • MEMS scanning mirrors are one of the technologies for implementation of laser beam scanning. MEMS mirrors are manufactured using semiconductor technology which facilitates high volume manufacturing, repeatable performance and low cost. Additional attributes of the MEMS scanning mirror technology are high tolerance to vibration and operational environment, accurate/rapid scanning, electronic control of scanning mirror position and small volume.
  • FIG. 14 includes a schematic functional block diagram which illustrates a LiDAR system 200 using step-frequency-modulation (FM) pulse-burst transmit envelope modulation and quadrature demodulation and a MEMS scanning mirror, according to some exemplary embodiments.
  • System 200 of FIG. 14 is identical to system 100 illustrated in FIG. 6A and described in detail above, with the exception of the addition of the MEMS scanning mirror capability.
  • Like features between system 100 of FIG. 6 A and system 200 of FIG. 14 are indicated by like reference numerals. Detailed description of features common to both system 100 of FIG. 6 A and FIG. 200 of FIG. 14 will not be repeated.
  • FIG. 15 includes a detailed schematic diagram illustrating MEMS scanning mirror transmit beam pattern as employed in the LiDAR system 200 of FIG. 14, according to some exemplary embodiments.
  • FIG. 15 schematically illustrates the transmit beam pattern 282 of MEMS scanning mirror 210, as processed via the transmit optics, according to exemplary embodiments.
  • system 200 is the same as system 100 of FIG. 6 A, with the exception of the scanning mirror capability.
  • a MEMS mirror controller/driver 216 provides a mirror drive signal 212 to MEMS mirror 210 on line 214, which causes MEMS mirror 210 to rotate about an axis 211, which can be oriented to provide azimuthal or elevational rotation of MEMS mirror 210.
  • signal mirror drive signal 212 can be substantially sinusoidal.
  • MEMS scanning mirror 210 tilts to allow high-speed, controlled beam steering in LiDAR range and image applications, as well as a number of other optical systems.
  • the narrow beamwidth, as represented in FIG. 15, and rapid azimuthal or elevational scanning of MEMS scanning mirror 210 are applicable to high bearing resolution scanning requirements.
  • the step-FM pulse-burst envelope modulation waveform of the present disclosure is well suited to provide complementary high range-resolution and is compatible with the scan rate of MEMS mirror 210.
  • step-FM pulse-burst modulation signal 115 is used by pulse modulator 174 to modulate substantially sinusoidal signal 187 to generate pulsed substantially sinusoidal signal 111.
  • the resulting pulsed modulated signal 111 from pulse modulator 174 is applied as a modulation signal to a laser modulator 176, which generates a control/modulation signal 117, which is applied to light emitter 178 to generate a step-FM pulse-burst modulated optical signal.
  • the step-FM pulse-burst modulated optical signal is transmitted to MEMS mirror 210 along optical path 240, where it is reflected by MEMS mirror 210 along optical path 242 to transmit optics 280, by which the step-FM pulse-burst modulated optical signal is transmitted to the one or more target objects in the transmit beam pattern 282 of MEMS scanning mirror 210.
  • FIG. 16 includes schematic time diagrams illustrating the data acquisition process of LiDAR system 200 utilizing MEMS scanning mirror 210, according to exemplary embodiments.
  • the top diagram in FIG. 15 illustrates the scan angle, i.e., angular position, of MEMS mirror 210 over time during data acquisition, and the bottom diagram illustrates the step-FM pulse-burst frequency over time during data acquisition.
  • a single, fixed-frequency, pulse-burst cluster is employed at each scan increment for the duration of each scan.
  • the frequency of the fixed-frequency pulse-burst cluster increases by the step frequency, Af, upon successive scans.
  • FIG. 15 illustrates the synchronization of the pulse burst frequency and the MEMS scanning mirror 210 angular position as scanning mirror 210 beam is scanned.
  • data is acquired for each beam position, i.e., scan increment, at each discrete frequency step.
  • the MEMS mirror position is non-linear with time.
  • the effect engenders a linear or synchronized pulse burst relationship with the mirror position.
  • MEMS mirror controller/driver 216 provides synchronization of the pulses of step-FM pulse-burst modulation signal 115, and, as a result, the optical illumination pulses of the step-FM pulse-burst modulated optical signal, with the angular position of MEMS scanning mirror 210.
  • FIG. 17 includes a schematic detailed functional block diagram of MEMS mirror controller/driver 216, according to some exemplary embodiments.
  • FIG. 18 includes a schematic time diagram illustrating synchronization of the step-FM modulation pulses with scanning mirror position provided by MEMS mirror controller/driver 216, according to some exemplary embodiments.
  • Mirror Cycle X2 turns high when the scan starts, which is when MEMS mirror 210 is at its maximum angle, which is illustrated as being ⁇ 12 degrees, by way of exemplary illustration only. It switches low again when MEMS mirror 210 is at its neutral or zero-degree position.
  • Mirror Cycle can be used to determine whether mirror 210 moving to the left or right (in the case of azimuthal scanning) or up or down (in the case of elevational scanning). The rising and falling edges of the Mirror Cycle signal coincide with the zero crossings of MEMS mirror 210.
  • synchronization between the scanning mirror position and the pulse burst transmission time is implemented, according to some exemplary embodiments.
  • One technique for synchronization is to divide the time between the start and stop position scan signals into many smaller, equal-time increments which approximate the angular position of scanning mirror 210. The division may be accomplished with a phase-locked loop (PLL) 252 configured as a frequency multiplier. The output of the PLL frequency multiplier 252 is applied to a counter 254, which acts as a frequency divider.
  • PLL phase-locked loop
  • counter 254 output value represents the time of the scan from which the angular position of mirror 210 may be calculated using a cosine function or determined from a look-up table (LUT), as illustrated by 256.
  • the mirror direction is determined using a D-flip-flop 258 and the synchronized transmission pulse burst is thus generated.
  • PLL 252 generates a clock from the Mirror Cycle X2 signal.
  • PLL 252 is configured to divide this single pulse into, for example, 1024 shorter pulses, uniformly spaced in time. These pulses are routed to counter 254, the current value of which corresponds to the time of the scan.
  • the angular position of scanning mirror 210 can be calculated using the cosine function or determined from a look-up table (LUT), as illustrated by 256.
  • LUT look-up table
  • the synchronized train of pulses 215 is generated by DSPC 268.
  • the output of D-flip-flop is applied on lines 218 to DSPC 268, and the output of LUT/cosine function 256, indicative of mirror position, is also applied on lines 218 to DSPC 268.
  • the mirror drive signal 212 also output from LUT/cosine function 256, is applied on lines 214 to MEMS scanning mirror 210 to control its rotation.
  • the FFT sample rate can be adjusted.
  • the FFT sample rate can be adjusted to twice the scan time.
  • FIGs. 19A through 19D include a series of four illustrative data matrices for the scanning mirror data acquisition, according to some exemplary embodiments.
  • FIG. 20 includes a table of parametric data in a typical automotive operational scenario of LiDAR system 100 using a MEMS scanning mirror for data acquisition, according to some particular exemplary embodiments.
  • the data acquisition process for the MEMS scanning mirror includes filling or populating n data matrices of dimension k x N; where n is the number of scans (also the number of frequency steps), k is the number of scan increments, and N is the number of range bin samples.
  • laser transmitter step-FM pulse-burst envelope modulation and receiver quadrature demodulation techniques pursuant to direct detection LiDAR systems have been described in detail.
  • Data acquisition techniques and signal processing gain have also been described in detail.
  • the technique of transmit envelope modulation in conjunction with receive quadrature demodulation as applied to direct detection LiDAR systems has been demonstrated to provide signal processing gain as determined by the increase in the signal-to-noise ratio at the system detection stage.
  • Significant operational factors include the change in transmission phase shift of the envelope modulation waveform over the two-way range to the object, and coherent detection of the envelope modulation waveform within the quadrature demodulator.
  • the envelope modulation waveform is derived from the quadrature demodulation local oscillator, thereby establishing the coherent signal required for detection.
  • step-FM pulse burst envelope modulation waveform of the present disclosure has been demonstrated to be compatible with MEMS fast scanning mirror.
  • FIG. 21 includes a schematic perspective view of an automobile 500, equipped with one or more LiDAR systems 100, 200, described herein in detail, according to exemplary embodiments.
  • LiDAR system 100, 200 is illustrated, it will be understood that multiple LiDAR systems 100, 200 according to the exemplary embodiments can be used in automobile 500.
  • LiDAR system 100, 200 is illustrated as being mounted on or in the front section of automobile 500. It will also be understood that one or more LiDAR systems 100, 200 can be mounted at various locations on automobile 500.
  • FIG. 22 includes a schematic top view of automobile 500 equipped with two LiDAR systems 100,200, as described above in detail, according to exemplary embodiments.
  • a first LiDAR system 100A, 200A is connected via a bus 560, which in some embodiments can be a standard automotive controller area network (CAN) bus, to a first CAN bus electronic control unit (ECU) 558 A.
  • CAN standard automotive controller area network
  • ECU electronic control unit
  • a second LiDAR system 100B, 20B is connected via CAN bus 560 to a second CAN bus electronic control unit (ECU) 558B.
  • ECU 558B Detections generated by the LiDAR processing described herein in detail in LiDAR system 100B, 200B can be reported to ECU 558B, which processes the detections and can provide detection alerts via CAN bus 560.
  • this configuration is exemplary only, and that many other automobile LiDAR configurations within automobile 500 can be implemented. For example, a single ECU can be used instead of multiple ECUs. Also, the separate ECUs can be omitted altogether.
  • the present disclosure describes a LiDAR system installed in an automobile. It will be understood that the system of the disclosure is applicable to any kind of vehicle, e.g., bus, train, etc., or the LiDAR system of the present disclosure need not be associated with any kind of vehicle.

Abstract

Un système LiDAR comprend un générateur de signaux destiné à générer un signal de sortie ayant une fréquence variable. Un circuit de modulation reçoit le signal de sortie du générateur de signaux et module le signal de sortie afin de générer un signal d'enveloppe à modulation pulsé conçu de façon à comprendre une pluralité d'impulsions, au moins deux impulsions de la pluralité d'impulsions ayant au moins deux fréquences différentes respectives. Le circuit de modulation applique le signal d'enveloppe à modulation pulsé à un signal optique pour générer un signal optique à modulation d'enveloppe d'impulsions comprenant une pluralité d'impulsions modulées par le signal d'enveloppe à modulation pulsé. Des éléments de transmission optiques transmettent le signal optique à modulation d'enveloppe d'impulsions dans une région. Des éléments de réception optiques reçoivent des signaux optiques réfléchis de la région. Des circuits de traitement de signaux de réception reçoivent les signaux optiques réfléchis et utilise la détection en quadrature pour traiter les signaux optiques réfléchis.
PCT/US2017/033271 2016-05-24 2017-05-18 Procédé et système lidar à détection directe avec transmission à modulation d'enveloppe de salves d'impulsions à modulation de fréquences (fm) échelonnées et démodulation en quadrature WO2017205171A1 (fr)

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